Direct reduction processes for producing metallized iron from iron oxide pellets, lump ores, or similar materials which include iron oxide, are widely known and used in the steel industry. Suitable direct reduction processes for forming metallized iron are disclosed in U.S. Pat. Nos. 3,128,174 and 3,881,916. In a direct reduction process such as the Midrex direct reduction process, pellets of metal oxides and/or lump ores are charged into the top of a shaft furnace to establish gravitational flow therethrough. Reducing gas consisting essentially of carbon monoxide and hydrogen is heated to sufficient temperature to effect direct reduction, is introduced to the metal oxide burden in the furnace, ascends through the burden in counter-flow relation to the gravitationally descending burden, and reacts with the burden, forming metallized pellets and a reacted top gas consisting principally of carbon dioxide and water along with some unreacted reductants, which are drawn off as sulfur-containing spent top gas. The resulting hot metallized product descends into the cooling zone of the furnace wherein it is cooled by contact with cool gas injected into the cooling zone. Cold direct reduced product is discharged from the bottom of the furnace.
Additionally, U.S. Pat. No. 3,748,120 discloses a shaft furnace direct reduction process in which spent reduction gas is catalytically reformed from a mixture of gaseous hydrocarbon and spent reducing gas from the reduction process. In this process the spent reducing gas is cleaned and cooled upon exiting the reduction furnace and prior to being introduced into a catalyst containing reformer. In the direct reduction process the reducing gas passes through and reacts with the burden to produce sulfur containing gases which contaminate the catalyst. Sulfur contamination of the catalyst lowers the overall efficiency of the process. Processes for reducing the sulfur level in the recycled spent reducing gas by increasing the metallic ion content of the scrub water utilized by the cooler-scrubber are also known.
The present invention provides an improved method and apparatus for reducing the sulfur contamination of the gas reformer catalyst by removing sulfur compounds from the spent process gas stream by reaction with chlorine dioxide prior to reintroduction of the process gas into the hot gas reformer.